The answer depends on which time period your game is. While there are a lot of early materials describing Krynnspace and travel between that crystal sphere and many others was detailed, later AD&D 2e material differed. In particular, after the publication of the novel Dragons of Summer Flame in 1995, Dragonlance setting enters the Fifth Age, the Age of Mortals. TSR's default line of DL products starts to use the SAGA system; while the published modules keep on supporting AD&D.
As a concrete example, consider the AD&D 2e sourcebook A Guide to the Ethereal Plane (TSR 2633) published in 1998. It clearly states that access the Krynn is blocked against ethereal travel:
Chant is that this world fell under the sway of some chaotic power. No one knows if that's the dark of it, but fact is, a body can't reach Krynn any longer. Many bloods've tried, but they all return rattling their bone-boxes about ether gaps and creatures born out of chaos. If that's the truth, then the Border area around Krynn's been blocked.
Phlogiston's relationship with the border ethereal is not very clear to me, but I believe the block would also apply to spelljamming as well.